Problem: Influenza infection results in high morbidity and mortality. Young children are at particular risk for incomplete influenza vaccination because, depending on their previous vaccination status, many need 2 doses in a single season, as one dose does not confer adequate protection. Yet, only half of those who receive the first dose receive the second. Besides forgetting to remember to return for subsequent doses, receipt of 2 doses in a season can be affected by limited parental knowledge regarding influenza vaccination such as lack of understanding of the need for a second dose, as well as the importance of prompt receipt of that dose. Even among disadvantaged populations, 90% of adults in the U.S. have a cellphone. In a scalable, efficient manner, text messaging can provide vaccine reminders that can both remind families to return for a second dose as well as offer educational information that can promote influenza vaccine health-literacy by addressing common barriers that result in missing or delaying a second dose. Our research in one low-income, urban primarily Dominican community has demonstrated the efficacy of using text message reminders to increase receipt of 2nd dose of influenza vaccine compared to solely a written reminder (72.2% vs. 57.7%; p<0.01). While previous text message vaccine reminder studies have demonstrated success, they have been conducted locally and primarily with a low-income population. A study with national scope is therefore vital to understanding the effectiveness and optimal use of text message reminders to parents with varied backgrounds and whose children are cared for in diverse practice settings. To achieve this goal, the proposed study has 3 specific aims: AIM 1: To compare the effectiveness i n improving receipt of the second dose of influenza vaccine of personalized text message reminders embedded with educational information vs. usual care in a diverse pediatric population in need of two doses in a given season. AIM 2: To compare the effectiveness i n improving t h e timeliness of the second dose of influenza vaccine of personalized text message reminders embedded with educational information vs. usual care in a diverse pediatric population in need of two doses in a given season. AIM 3: To assess parental and child characteristics that modify text message effectiveness. Methods: In each of 2 seasons, 2000 parents of 6 months through 8 year-old children in need of two doses that season (4000 total) in 50 practices nationally who have received the 1st influenza vaccine dose that season will be randomized to receive either 1) text message reminders embedded with influenza vaccine health-literacy promoting information or 2) usual care. Parents will be recruited through the American Academy of Pediatrics national Pediatric Research in Office Settings (PROS) network. Outcomes: The primary outcome is receipt of two doses by the end of the season (April 30). A secondary outcome will be timeliness of second dose receipt. If successful, this project could support and inform a new paradigm in interactive health communication in a low cost, scalable manner that may be readily disseminated.